The invention relates to a surface aerator equipped with a central vertical shaft which can be coupled to a drive means, substantially vertical blades being mounted on the lower end of said shaft.
Surface aerators of this type are well known in the art and are rotated on the level of a surface of liquid so as to stir the liquid and aerate it by creating a large interfacial area between the air and the liquid. These surface aerators are frequently used in aerating tanks of activated sludge systems, where the tank may have the form of a rectangular vessel or of a closed circuit.
Surface aerators must satisfy a number of important demands if optimum effectiveness is to be achieved. First of all, they must be marked by a high oxygen input efficiency, which is defined as the number of kilograms of oxygen introduced per kWh consumed. This oxygen input efficiency must furthermore have a maximum of constancy over the range of depths of immersion and the range of speeds required for controlling the capacity. Moreover, the surface aerators must possess an output of capacity of maximum stability in service conditions as well as an adequate propelling capacity.
The known surface aerators often have the drawback of insufficiently meeting all of the aforementioned demands and, specifically, of lacking a high oxygen input efficiency.